Tuesday, April 29, 2014

Greetings,
Tonight's workshop was once again a good time. We had 6 people show tonight. One was a new member that had come to us from our website. He has acquired an older LX3 Meade Schmidt-Cassegrain 8" scope and tripod. The reason for his visit was that he can see what looks like mold or fungus on the optics that has been put away, dormant for a long time. I recommended he talk with our equipment rangler to get a little guidance on trying to get this up and running. I will BCC this email to all of interested parties. I think he will be leaving SB in the near future and he would really like it if his wife could get a look at the rings of Saturn before he leaves, I think we can help that to happen.

Anyway, the other reason for the email is to let you all know once again that this kind of email you will get that informs us all if and when we will meet for a workshop. These normally take place on Tuesdays from 7:30-9 pm in the Broder Building, across the creek at the Museum of Natural History. These fine people at the Museum allow us to meet here on a regular basis to advance our skills of mirror making, scope building, Astro imaging and just about everything else that envelops the world of optics and scope building and testing. Please feel free to come by and see what we are about. We will surprise you, I promise.

T

On 4/30/2014 8:42 AM, Tim C wrote:

Hi TomT,
Sorry you could not make it. I worked for a very short time last night because a new person showed up. His name is Matt. I asked how he came to find our workshop. He said he googled SBAU.org and found out about our workshop. That's pretty cool huh. I don't know if I'd use his name in the blog without permission as I told him I'd use his email address in a blind fashion. [first names + maybe last initial is enough and keeps privacy. tt]

I think what was striking about last night is that he has inherited an older LX3 Meade 8" Schmidt. It has been sitting around though for an extensive time so it has gotten some fungus or mold on the optics. Matt will bring this scope next week and we may take a look at it. As I am not an expert on Schmidt-Cassegrains and certainly not abreast of the techniques for removing mold, I let Matt know that we will refer the issue to Art, Tom W. A and Jerry. That was one thing.

Mike also brought this light you see below. It looks really nice for a light
source for our testers. The only thing is it has to be pointed right at
the mirror or you don't see it. It kind of has a long barrel. Mike has
some ideas on this.

Christopher brought in his mirror to start polishing
but he didn't do anything. Next week he will bring a work surface and
clamps to tie it down and begin trying to correct his edge on his
mirror. Tom and Jerry will advise him of strokes to use.
T

Thanks for coming on by last night. We had to move to classroom 1 because of a mixer that had been scheduled for Broder. This is an example of what I have alluded to in the past. From time to time we have to give way to events that are scheduled ahead of time in Broder. Much thanks to Bill C who tried to give me advanced notice. Sorry Bill- I did not give you my new number and that is now corrected. Bill made it so easy for us to shift over to the classroom. I want to let you all know, the classroom is the fallback room we use in case Broder is busy. I try to leave a note on the door of Broder ( the door nearest the footbridge) telling where we will be or if (as in some rare cases) the workshop will be cancelled.

Once we carefully moved a couple of items from 2 tables, we set up a Ronchi test for Christopher's 10" mirror. (Used to be Chuck's "Mr. Peanut".) Wow! Chuck had really come a long way since I last saw this mirror! Part of my reason for the follow up email is to inform 2 head pros in our workshop, Tom W. and Jerry W. of the results we looked at. Christopher is using a sub diameter lap to polish this mirror out and some of the correction strokes, I am not qualified to answer to. So, Tom and Jerry ( I always like saying that), we saw an almost perfect sphere that has a turned down edge way out at the 97-100% zone. For you in the workshop unfamiliar with what I am talking about, the dreaded "turned down edge" is a typical result of grinding and polishing your own mirror. Imagine your polishing your mirror and testing it with a glass slide that has etched lines that are parallel. If your mirror is perfectly spherical, you will see parallel vertical lines extending from edge to edge. But, if those lines turn at the edge, you have a turned down edge (TDE). Tom or Jerry have always told me that you must not think of the edge as low but instead think of the adjacent zone as high. Okay, now confused? Just think of this. What Chris will want to do to correct this is work on the adjacent zone to the inside of this turned edge. Work it all the way around the mirror, just as you would polish by using strokes that are predictably random. Now if you think about it, this will lower the adjacent zone to the level of the edge and now you have corrected the edge. I can hear you all say, "but the middle has not been worked on and now you have a high middle". Correct! But it is much easier to correct the middle than a TDE. What type of stroke to use and for what duration, I will leave for our experts. Tom Totton took some images of this last night and if he would be so kind he may send these to Tom and Jerry to look at.

Last night, speaking of TomT, we also took a photo of members of our group in the Planetarium. It was really fun watching Tom set up a make shift platform for his timed shot and scramble over to get in the picture. He had to fiddle a bit to get the big planet Jupiter to show in the photo. This added some seconds to the shot. Tom kept leaving the shot early and we really enjoyed his ghost like figure leave the photo. One thing I thought of only now Tom is that this was in honor of Earth Day and you used Jupiter in the photo. Now we'll have to wait another year to set it up again!

Anyway, a good time was had by all. Paul W asked me a while back to get permission to use images and diagrams from the Stellafane website. I told him last night they just responded and told me it was okay as long as it is not in a commercial form. I want to finish though by thanking Paul for all his hard effort on the club website. He told me last night he just completely re-did the whole site (40hours +!!!!!) thank you so much Paul from all of us. You members out there, spread the news. And use the forum! In fact, Tom W. told me members are using the newsletter to sell equipment. Please know you can use the Forum and reach a whole lot more people!

See you all soon. Remember, May 10th is Astronomy Day. We will be out at Calle Real Market Place. I have a permanent shoulder injury and it would be great to see a few of you spell me with mirror grinding. TimC

"Digital color cameras generally use a Bayer mask over the CCD. Each square of four pixels has one filtered red, one blue, and two green (the human eye is more sensitive to green than either red or blue). The result of this is that luminance information is collected at every pixel, but the color resolution is lower than the luminance resolution.
Better color separation can be reached by three-CCD devices (3CCD) and a dichroic beam splitter prism, that splits the image into red, green and blue components. Each of the three CCDs is arranged to respond to a particular color. Many professional video
camcorders, and some semi-professional camcorders, use this technique,
although developments in competing CMOS technology have made CMOS
sensors, both with beam-splitters and bayer filters, increasingly
popular in high-end video and digital cinema cameras. Another advantage
of 3CCD over a Bayer mask device is higher quantum efficiency
(and therefore higher light sensitivity for a given aperture size).
This is because in a 3CCD device most of the light entering the aperture
is captured by a sensor, while a Bayer mask absorbs a high proportion
(about 2/3) of the light falling on each CCD pixel."

Paul showed his photo collage taken during the lunar eclipse late Monday night.

Dmitrii polishing his 12.5 mirror; Jerry says it needs 3 hours more to smooth it, then pay attention to the surface figuring.

Tim showing star hopping PowerPoint slideshow to Chris and all. He has some funny cartoon pictures on the charts to make them more memorable. Tim is also putting time in on grinding the 8" donated mirror, minimizing any concern with the pits left previously.

Sunday, April 13, 2014

Because we have a lunar eclipse the night of April 14th&
15th, some of our plans may have to be put on hold once again.
Regardless though, the grinding/polishing will continue on.

So, for this week's food for thought- I recently went to La
Sumida Nursery with my wife to look for our annual project of tomato
growing. There, we spotted whole wine kegs-you know, the same ones you
see outside the Broder Building. These would make great work platforms
for mirror grinding. So, why would I like these over the traditional oil
drums? Easy- I'm married to a spouse who does not think oil drums are
an attractive feature to use in the garden. But, a wine cask is just the
right touch for esthetic surroundings. These may work! Okay, they are
not the only work top we can use but please indulge me for a moment.
They have a recessed top that needs to have a work top placed so mirror
grinding can take place ( a wood working challenge). I will suggest
they would be a nice feature to use as a table for potted plants. But,
it also must morph into a workbench for grinding telescope mirrors. This
needs innovation.

Innovation- the one great attribute that all ATM's possess. This is really
is what this aside is all about then, isn't it? We all have to use our
minds to come up with solutions to problems we encounter in everyday
telescope construction. Come on, admit it! We all use the creative
spirit to make something from nothing- to utilize whatever we can get
from our network of ATM's or resources around us.

True, eh? What does this have to do with a wine cask? Okay, let's
get simple but creative. I told you the wine cask has a recessed top.
What can you suggest using to add a top that can be used for grinding
(without contamination) and then removed or modified to receive a potted
plant or whatever, so the "garden area" looks like this wine barrel
belongs? Simple huh? Not to me. But it does exemplify what we are
about. Innovation, creativity and.... Genius!

Friday, April 11, 2014

Looking at SBAU vs forum vs SBAUTW blog for placing Telescope Workshop notes. TomT says the more places information is posted the better.
Comparing cell phones for viewing drop down menus of SBAU.org...all seem to work, but drop downs may be in pop up window.

PaulW says Spectrum coatingshttp://www.spectrum-coatings.com/ can give 98% reflectivity "Max "R" (EAL)" "modified enhanced aluminum coating. It is not a "pure dielectric"
coating. One of the great benefits of this coating is it can etched like
a normal EAL or PAL coating. Therefore, if the coating does fail you
will not have to have the primary mirror polished to remove the film
(unlike a dielectric coating). A pure dielectric coating has no metal
layer, which means it cannot be etched off - it must be polished off
which would require re-figuring the primary mirror."

http://stellafane.org/tm/dob/ota/primary.html says:
"The absolute minimum criteria for an acceptable telescope mirror is that it be "diffraction limited" or
alternatively this can be stated as "a maximum error of ¼ wavelength of light". Both of these
terms refer to the Rayleigh Criterion, which actually should only be applied to complete telescopes, not
individual components (but each optical component must be at least as good).
A mirror that meets the ¼ quality level of reflected
light needs to have a surface accuracy twice as good (in this
case 1/8 wave)."

-DavidH trying to tighten Allen screws on old Celestron mount motors;
worm gear was seizing otherwise. Orion Skyview Pro, per BruceM, seems
identical and info may be available on internet. (see maybe this: http://www.company7.com/orion/mounts/orionsvpmount.html ; see manual near bottom of page)

-Dmitriiz polishing his 12.5" about 30 minutes until his solution ran out.

-TimC grinding at 500 after removing worst of last week's scratch at 320 grit.
-TimC working on next "From the Workshop" #5 notes regarding parabolic shape and mirror strokes.

-TomW melting more pitch for pouring small tool for ChrisU polishing of 10", but Chris had to go back home to get the mirror for forming the pitch lap properly.

-BruceM purchased a Celestron C8 orange tube OTA ($292, ebay?) with
dovetail mount for improvement over his 5", but will see if mirror
condition needs attention.

On 4/1/2014 11:40 PM, TimC wrote:

Thanks all for coming out this rainy Tuesday. We ended up with 13 people tonight. I have updated our workshop list and this is the main reason for this email. You will be receiving this type email before our workshop scheduled meetings or cancelations. We normally meet at the Broder Building across the walking bridge at The Museum of Natural History. We meet between 7:30-9pm each Tuesday.
Tonight we had a few guests that were very welcome. I hope they had a great time and were interested in the doings of our little group. There are many informed members that have a lot of information that you may be interested in or answers to questions you may have in many phases of telescope making as well as Astro imaging and much more!
Tonight for example of the goings on, we had one person polishing a 12.5" mirror, one person grinding an 8" mirror and a pitch lap being poured. Also, we had a person with parts of his mount and yet another showing his "Flaming Tomato", an 8" Dob. I just love it. What a great name for a scope!
Over the course of an evening many things may take place. I love the offshoot conversations that happen all the time. But I will just end this by saying sometimes when we get together we just find ourselves visiting, taking a deep breath and letting the whole roaring thing go by, settling in for comfortable conversation that just drifts from topic to topic, till finally we must gather ourselves once more and return to the moment and bid ourselves well, until we meet again.
And so.... till we meet again,
T